1. Field of the Invention
The present invention relates to a structure of a tire for a motorcycle.
2. Description of the Related Art
In recent years, a motorcycle can carry out high speed running with an increase in the displacement of an engine, and the size and weight have been increased. For this reason, an enhancement in performance has increasingly been required for motorcycle tires. The body of the motorcycle is greatly tilted during cornering. Therefore, it is necessary to design a tire which generates a proper cornering force and camber thrust when it rolls at a tilt with respect to a road surface.
In the case in which only the cornering of the motorcycle is taken into consideration, a high stiffness is maintained in the shoulder portion of the tire so that stable high speed cornering can be implemented. In the tire for the motorcycle, however, the stiffness of the center portion of a tread is generally increased with an enhancement in the stiffness of the shoulder portion. However, by providing the tire with a center portion having a high stiffness, the straight running stability of the motorcycle is hindered.
Conventionally, the high stiffness of the shoulder portion in the tire for a motorcycle has been maintained, and at the same time, the stiffness of the center portion has been required to be reduced more greatly than that of the shoulder portion. In order to meet the demand, various proposals have been made in Japanese Laid-Open Patent Publication No. 10-181310, Japanese Laid-Open Patent Publication No. 5-246210 and U.S. Pat. No. 5,441,093.
In a conventional tire for a motorcycle which has been provided in order to cause the straight running stability and high speed cornering property to be compatible with each other, an enhancement in the stiffness of the shoulder portion and the suppression of the stiffness of the center portion are not always well-balanced, and thus the straight running stability and the high speed cornering property are not compatible with each other on a high level. The structural continuity of a tread portion and the center portion is not always achieved. For this reason, in a running state for a transition period from straight running to cornering and a transition period from the cornering to the straight running, linearity is maintained with difficulty.
It is an object of the present invention to provide a tire for a motorcycle in which straight running stability and high speed cornering y in a motorcycle can be caused to be compatible with each other at a high level, and furthermore, excellent linearity can be implemented in the transition from straight running to cornering or from cornering to straight running.